1,367 research outputs found
Quasi-Localization of Gravity by Resonant Modes
We examine the behaviour of gravity in brane theories with extra dimensions
in a non-factorizable geometry. We find that for metrics which are
asymptotically flat far from the brane there is a resonant graviton mode at
zero energy. The presence of this resonance ensures quasi-localization of
gravity, whereby at intermediate scales the gravitational laws on the brane are
approximately four dimensional. However, for scales larger than the lifetime of
the graviton resonance the five dimensional laws of gravity will be reproduced
due to the decay of the four dimensional graviton. We also present a simple
classification of the possible types of effective gravity theories on the brane
that can appear for general non-factorizable background theories.Comment: 8 pages, 3 figures included. Requires JHEP.cls. Typos fixed, note and
references added. Added expression for width of resonanc
How Well Does AdS/QCD Describe QCD?
AdS/QCD is an extra-dimensional approach to modeling hadronic physics,
motivated by the AdS/CFT correspondence in string theory. AdS/QCD models are
often more accurate than would have been expected at energies below a few GeV.
We address the question of why these models are so successful, and respond to
some of the criticisms that have been waged against these models.Comment: To appear in proceedings of Crossing the Boundaries: Gauge Dynamics
at Strong Coupling (Shifmania), Minnesota, May 14-17, 2009. 12 pages, 2 eps
figure
Necessary and sufficient conditions for non-perturbative equivalences of large N orbifold gauge theories
Large N coherent state methods are used to study the relation between U(N)
gauge theories containing adjoint representation matter fields and their
orbifold projections. The classical dynamical systems which reproduce the large
N limits of the quantum dynamics in parent and daughter orbifold theories are
compared. We demonstrate that the large N dynamics of the parent theory,
restricted to the subspace invariant under the orbifold projection symmetry,
and the large N dynamics of the daughter theory, restricted to the untwisted
sector invariant under "theory space'' permutations, coincide. This implies
equality, in the large N limit, between appropriately identified connected
correlation functions in parent and daughter theories, provided the orbifold
projection symmetry is not spontaneously broken in the parent theory and the
theory space permutation symmetry is not spontaneously broken in the daughter.
The necessity of these symmetry realization conditions for the validity of the
large N equivalence is unsurprising, but demonstrating the sufficiency of these
conditions is new. This work extends an earlier proof of non-perturbative large
N equivalence which was only valid in the phase of the (lattice regularized)
theories continuously connected to large mass and strong coupling.Comment: 21 page, JHEP styl
Form Factors and Wave Functions of Vector Mesons in Holographic QCD
Within the framework of a holographic dual model of QCD, we develop a
formalism for calculating form factors of vector mesons. We show that the
holographic bound states can be described not only in terms of eigenfunctions
of the equation of motion, but also in terms of conjugate wave functions that
are close analogues of quantum-mechanical bound state wave functions. We derive
a generalized VMD representation for form factors, and find a very specific VMD
pattern, in which form factors are essentially given by contributions due to
the first two bound states in the Q^2-channel. We calculate electric radius of
the rho-meson, finding the value _C = 0.53 fm^2.Comment: 7 pages, RevTex. References were added, some modifications in the
text were mad
Dimension Six Corrections to the Vector Sector of AdS/QCD Model
We study the effects of dimension six terms on the predictions of the
holographic model for the vector meson form factors and determine the
corrections to the electric radius, the magnetic and the quadrupole moments of
the rho-meson. We show that the only dimension six terms which contribute
nontrivially to the vector meson form factors are X^2F^2 and F^3. It appears
that the effect from the former term is equivalent to the metric deformation
and can change only masses, decay constants and charge radii of vector mesons,
leaving the magnetic and the quadrupole moments intact. The latter term gives
different contributions to the three form factors of the vector meson and
changes the values of the magnetic and the quadrupole moments. The results
suggest that the addition of the higher dimension terms improves the
holographic model.Comment: 6 pages, RevTex, revised version, accepted for publication in Physics
Letters
High resolution HLA analysis reveals independent class I haplotypes and amino-acid motifs protective for multiple sclerosis.
We investigated association between HLA class I and class II alleles and haplotypes, and KIR loci and their HLA class I ligands, with multiple sclerosis (MS) in 412 European American MS patients and 419 ethnically matched controls, using next-generation sequencing. The DRB1*15:01~DQB1*06:02 haplotype was highly predisposing (odds ratio (OR) = 3.98; 95% confidence interval (CI) = 3-5.31; p-value (p) = 2.22E-16), as was DRB1*03:01~DQB1*02:01 (OR = 1.63; CI = 1.19-2.24; p = 1.41E-03). Hardy-Weinberg (HW) analysis in MS patients revealed a significant DRB1*03:01~DQB1*02:01 homozyote excess (15 observed; 8.6 expected; p = 0.016). The OR for this genotype (5.27; CI = 1.47-28.52; p = 0.0036) suggests a recessive MS risk model. Controls displayed no HW deviations. The C*03:04~B*40:01 haplotype (OR = 0.27; CI = 0.14-0.51; p = 6.76E-06) was highly protective for MS, especially in haplotypes with A*02:01 (OR = 0.15; CI = 0.04-0.45; p = 6.51E-05). By itself, A*02:01 is moderately protective, (OR = 0.69; CI = 0.54-0.87; p = 1.46E-03), and haplotypes of A*02:01 with the HLA-B Thr80 Bw4 variant (Bw4T) more so (OR = 0.53; CI = 0.35-0.78; p = 7.55E-04). Protective associations with the Bw4 KIR ligand resulted from linkage disequilibrium (LD) with DRB1*15:01, but the Bw4T variant was protective (OR = 0.64; CI = 0.49-0.82; p = 3.37-04) independent of LD with DRB1*15:01. The Bw4I variant was not associated with MS. Overall, we find specific class I HLA polymorphisms to be protective for MS, independent of the strong predisposition conferred by DRB1*15:01
Black Diamonds at Brane Junctions
We discuss the properties of black holes in brane-world scenarios where our
universe is viewed as a four-dimensional sub-manifold of some
higher-dimensional spacetime. We consider in detail such a model where
four-dimensional spacetime lies at the junction of several domain walls in a
higher dimensional anti-de Sitter spacetime. In this model there may be any
number p of infinitely large extra dimensions transverse to the brane-world. We
present an exact solution describing a black p-brane which will induce on the
brane-world the Schwarzschild solution. This exact solution is unstable to the
Gregory-Laflamme instability, whereby long-wavelength perturbations cause the
extended horizon to fragment. We therefore argue that at late times a
non-rotating uncharged black hole in the brane-world is described by a deformed
event horizon in p+4 dimensions which will induce, to good approximation, the
Schwarzschild solution in the four-dimensional brane world. When p=2, this
deformed horizon resembles a black diamond and more generally for p>2, a
polyhedron.Comment: 13 pages, 1 figure, latex, JHEP.cl
Small volume expansion of almost supersymmetric large N theories
We consider the small-volume dynamics of nonsupersymmetric orbifold and
orientifold field theories defined on a three-torus, in a test of the claimed
planar equivalence between these models and appropriate supersymmetric ``parent
models". We study one-loop effective potentials over the moduli space of flat
connections and find that planar equivalence is preserved for suitable averages
over the moduli space. On the other hand, strong nonlinear effects produce
local violations of planar equivalence at special points of moduli space. In
the case of orbifold models, these effects show that the "twisted" sector
dominates the low-energy dynamics.Comment: 20 pages, 3 figures; added references, minor change
Conformal Symmetry and the Three Point Function for the Gravitational Axial Anomaly
This work presents a first study of a radiative calculation for the
gravitational axial anomaly in the massless Abelian Higgs model. The two loop
contribution to the anomalous correlation function of one axial current and two
energy-momentum tensors, , is computed
at an order that involves only internal matter fields. Conformal properties of
massless field theories are used in order to perform the Feynman diagram
calculations in the coordinate space representation. The two loop contribution
is found not to vanish, due to the presence of two independent tensor
structures in the anomalous correlator.Comment: 34 pages, 5 figures, RevTex, Minor changes, Final version for Phys.
Rev.
Deficits in Beam-Walking After Neonatal Motor Cortical Lesions are not Spared by Fetal Cortical Transplants in Rats
Adult rats that sustained unilateral motor cortical lesions at birth demonstrated deficits in traversing an elevated narrow beam. These deficits, manifested by hindlimb slips off the edge of the beam, were not spared in animals that received fetal cortical transplants into the lesion cavity immediately after lesion placement
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